1. Field of the Invention
This invention relates to aerial refueling systems, and more particularly to aerial refueling systems which use a reel assembly to trail a hose through which fuel is transferred from a carrier aircraft to a receiver aircraft.
2. Description of Related Art
Aerial refueling dramatically increases the flight time and range of an aircraft. Refueling in flight saves time by eliminating the time consuming landing and take-off associated with refueling on the ground. It also saves fuel because an aircraft's fuel consumption is substantially higher while climbing than while cruising. As a result, an aircraft which is refueled in flight requires less time and less fuel to fly the same distance as an aircraft which is refueled on the ground. Additionally, an aircraft which is refueled in flight is not dependent on ground based facilities and can fly extended missions over areas where such facilities are unavailable.
Although conventional aerial refueling systems can be mounted directly within a carrier aircraft, they are most commonly contained within pods which are externally attached to the carrier aircraft. This eliminates the need for special tanker aircraft because any aircraft to which the refueling pod is attached can serve as a carrier aircraft. The pods may be of the "wet" variety, meaning that fuel is contained within the pod, or of the "dry" variety which requires an external fuel supply.
In conventional aerial refueling systems, refueling is accomplished by trailing a fuel supply hose from the carrier aircraft. The trailing end of the supply hose is provided with a pressure sensitive coupling drogue which is compatible with a connector on the receiving aircraft. The two aircraft are coupled by maneuvering them so that the drogue and the connector engage each other, fuel is then transferred from the carrier aircraft through the hose to the receiver aircraft. When the fuel transfer is complete, the planes are uncoupled and the hose is retracted. Several prior art refueling systems use reel assemblies to facilitate trailing and retracting the hose. In these systems, the hose is wrapped around the circumference of a drum shaped reel. The hose is trailed by rotating the reel such that the hose unwinds. The hose is retracted by reversing the direction of rotation and rewinding the hose.
One particular type of conventional refueling system uses a reel which rotates around an axis transverse to the direction of the trailing hose. However, in order to accommodate a hose which is long enough to allow the aircraft to maintain a safe distance during the refueling operation, the reel must be relatively long and the hose must be wrapped around the reel in multiple layers. As a result, the transversely mounted reel will only fit within a pod that has cross-sectional area which is too large to be carried by many tactical aircraft. Additionally, wrapping the hose in multiple layers tends to crush the lower layers resulting in damage to the hose. Because this damage occurs in the lower layers it is difficult to detect by visual inspection and may not be discovered until the pod is in operation. If this occurs, the fuel transfer operation may fail with the result that the mission must be aborted, possibly leaving the receiver aircraft without enough fuel to land safely.
Other refueling systems incorporate a hose reel which is mounted for rotation about an axis which is generally parallel to the trailing hose. This allows the use of a longer reel which can accommodate the necessary length of hose in a single layer. However, an axial reel requires a feeding device to change the direction of the hose from transverse of the drum for wrapping to axial of the drum for trailing. Previously, this has been accomplished by a carriage and sheave assembly. Conventionally, these assemblies usually require a number of support beams and guide rails to support the carriage and sheave in the proper position. The support beams and guide rails are mounted within the pod alongside the reel. As a result, the cross-section of this type of pod is still too large to be used with many types of aircraft.
Presently available refueling systems generally rely on hydraulic systems to supply power for rotating the reel. These systems are inherently bulky, heavy and require substantial maintenance. Additionally, it is very difficult to check the operational status of such systems prior to conducting a refueling operation.